Network Topologies - N10-008 CompTIA Network+ : 1.2

When you're designing, building, or

troubleshooting a network, you'll be

using a network topology type that can

vary depending on the technology you're

using. If you're looking to understand

the way the data is flowing, or you want

to plan to create a new type of network,

then it's useful to understand what

these topologies might be. This is also

useful during the troubleshooting

process because you'll know exactly what

flow the traffic takes to get between

point A and point B. One of the most

popular types of topologies is the star

topology. You might also hear this

referred to as a hub and spoke, where the

hub is in the middle and the spokes are

along the outside. This is a topology

that you'll find on almost any network,

regardless of the size of the network.

And you'll also find that most devices

are connecting back to this central hub

of the star. For example, a switched

Ethernet network has the Ethernet switch

in the middle of this star. And then all

of the devices run directly back to this

particular switch. They're not connecting

to each other. They're instead connecting

back to the central switch in this star

topology.

Although we don't often see a ring

topology used on our local area networks,

it's still a topology type that's used

quite often for wide area networks. So

although many people will remember the

older Token Ring technologies that we

used to run inside of our local area

networks, we don't generally find those

ring networks any longer. But if you're

connecting over a metropolitan area

network or a wide area network, we use

ring networks extensively. It's not

because a ring technology somehow lends

itself to work better over a wide area

network. It's because we can create

additional redundancy using the ring

topology.

For example, a very common way to send

traffic over a ring network is to have

the traffic simply go in a circle. Now, if

we're on this wide area network and

there's construction going on and

someone happens to sever a fiber

connection that's being used for this

metropolitan area network, then we're not

going to be able to send that traffic

through the rest of that ring. But the

devices that are on either side of that

severed link recognize that traffic is

no longer able to traverse that

connection, and instead will loop back

the connection on those individual

endpoints. So instead of having data go

around a ring, the data will instead go

as far as it can around the ring and

then loop back to get to the other side

of the ring, maintaining uptime and

availability even in the case where part

of that ring may be severed.

Early types of Ethernet networks were

not switched Ethernet, but were instead

run over coax. And this coax was quite

simply a cable that was run down the

middle of the room, very similar to this

cable. This is a bus network. And although

it was commonly used on those early

Ethernet networks, we can still find

modern networks that use the same bus topology.

One problem with bus networks is that it

is a single cable that is running either

through the walls or down the center of

the room. And if we happen to have a

break in this cable, you can see

immediately that it would suddenly

segment the network into different

pieces, or in some cases, cause no data to

be transferred across the network. That's

one of the reasons we moved away from

bus networks for our local area networks--

because one single disconnect could

cause an outage for everybody else on the network.

In our modern automobiles, we have bus

networks that we use extensively. These

are Controller Area Network buses, or CAN

bus connections, and they're used to

connect all of the different sensors and

controllers inside of our automobiles to

be able to make all of our cars much

safer to drive on the roads.

Another popular topology, especially in

larger networks, is to create a mesh

between devices or a mesh between sites.

We may have devices that are connected

in different locations, and we might want

to connect them all together. But instead

of having a single connection to a

particular site, we may want to create

multiple connections to mesh these

together. That way, if we do lose any one

of these network links, we're able to

work around that problem by simply using

one of the redundant connections.

You'll commonly use this type of mesh

design if you're creating redundancy or

fault tolerance, or perhaps you're

designing a load-balanced network and you

can use different parts of the network

to share that load.

Probably the most common place to find a

wired mesh network is over a wide area

network, where you can create multiple

links to other sites so that you can

have a primary connection from one site

to the other, and then a backup or

secondary connection that you can use if

you run into problems.

When you start combining these different

topologies together, you create a hybrid

network. A hybrid network is more than

one of these topology types all working

together. For example, you might have

three remote sites all connecting

devices together using a switched

Ethernet or star network. And then you

may be connecting those together over a

wide area network that uses a ring topology.

If you're using a wireless network, you

may be communicating in a number of

different ways. If you're using an access

point, you're probably communicating over

an infrastructure connection. This means

that all of the devices on your network

are communicating through an access

point. This is probably the most common

way to use wireless connections, but it's

not the only way to communicate over a

wireless link. If you just have two

devices and there's no access point that

you can use, you can connect directly

from one device to another using ad hoc

networking. You don't need an access

point or any other type of wireless

infrastructure. You simply have

one device communicate directly to another

device over this wireless connection.

And if you've added Internet of Things

devices, which are commonly wireless

devices that control our lights, our door

locks, or the air conditioning systems,

then you're probably using a mesh

network where all of these devices can

communicate to all the other devices

simultaneously to create an

interconnected mesh of communication

between all of these IoT devices.

One of the advantages of these mesh

wireless networks is that it allows many

devices to communicate to each other,

even if those devices are very far apart

from each other. This also allows the

mesh network to self-heal. So if you turn

off one of those IoT devices, the

remaining devices will self-heal and

redesign themselves into a mesh network

that will allow them to continue the communication.